This section examines both the chronology and destructive capacity of tsunamis in the Hawaiian Islands. Doing so provides a link in understanding steps toward building resilience to such events and reducing their impacts. Figure?
1
depicts the locations mentioned in the text. Section?
3.1
starts with the first historical accounts of tsunamis beginning in 1812 CE and runs through the nineteenth century, while Sects.?
3.2
and
3.3
cover twentieth and twenty-first century tsunamis, respectively (cf. Table
1
). The primary sources of data for these tsunamis include newspaper reports, missionary accounts and published documents. Field data from the historic period primarily include geochronological, microfossil and sedimentary, and geochemical analyses. Sections?
3.4
and
3.5
examine the Holocene (prior to the historic period) and Pleistocene records of tsunami impacts, respectively. The pre-historic evidence of tsunami impacts derives from ethnographic accounts and archaeological data as well as geochronological, microfossil, sedimentary, and geochemical evidence from field analyses (see Table
2
).
3.1
Regionally and locally generated historic tsunamis: 1812?1900 CE
The written record in Hawai?i, which starts in the 1820s, ushered in an era of historical documentation of tsunamis and other natural phenomenon. As noted above, the first record of a tsunami dates to December 21, 1812 CE, by Hawaiian historian John Papa ???, although he wrote his account as much as five decades after the event (Papa ???
1995
). Historical analysis indicates that this wave originated from the California coast, providing important insights into assessing the source of tsunami threats. For example, Atwater et al. (
2015
) ability to link the 1700 CE Cascadian subduction zone earthquake with an ‘orphan’ tsunami (an event not preceded by local seismic activity) on the east coast of Japan demonstrates the potential vulnerability of the Hawaiian islands to tsunamis from this source (Goff et al.
2022
).
Hawai?i’s first historically recorded deadly tsunami was generated by an earthquake off the coast of Valdivia, Chile. This wave struck the Hawaiian Islands at approximately 7:00 p.m. on November 7, 1837 CE. Historical reconstructions of this event have estimated current velocities in the town of Hilo, which received the bulk of the damaging impacts of the wave, of between 15 and 18?km/hour (Lander and Lockridge
1989
). Missionary accounts of the tsunami have proven especially helpful in reconstructing the physical and social impacts of the event. Two documented historical accounts come from American Congregational missionaries, one stationed at Hilo, Hawai?i, and the other at Wailuku, Maui (Fig.?
1
). Sarah Joiner Lyman’s account from Hilo, begins:
“As we were about to kneel for prayers in the evening we heard a great outcry among the natives on the beach [and] concluded that there was trouble among the sailors of an English ship now in port. As soon as the prayer was over Mr. L. [David Lyman, the author?s husband] went out to ascertain the cause of such confusion, when to our great surprise we found that the water in the bay had risen so as to go many rods beyond its usual bonds. A number of houses had been in an instant swept away and the inmates carried no one knew where... Some members of a family were carried in one direction and some in another. Some individuals were carried out so far in to the bay that they must have drowned, but for the aid of the ship’s crew now in port. They took 13 out of the water some of whom were much exhausted. Eight dead bodies have been found and others are missing…This is a solemn visitation and I believe the people feel it so…the prevailing impression seems to be among the people, that it is a judgement from God, on account of their disregarding his word” (reported in Lyman
1990
: 98).
The wave at Hilo took the lives of fourteen individuals and destroyed 66 homes. However, Lyman’s (
1990
) reported observation that residents understood the tsunami as both judgement and wrath suggest an important social dimension to this event. Tsunamis are often linked with profound social change, in this case by fostering a heightened sense of piety intended to avoid divine wrath (Goff and Nunn
2016
). As discussed below, Hawaiian myths and legends also suggest an association between cataclysmic events (presumably a tsunami) and profound social change.
The Rev. Richard Armstrong on Maui recorded his recollections of the 1837 CE event by noting its unexpectedness:
Footnote
1
“At about seven o'clock in the evening, the waves … gradually receded from the shore to a distance of some fifteen or twenty rods, leaving multitudes of fishes bare upon the ground, so that the children observing it ran and picked some of them up. The rush of the wave was so sudden and unexpected, that the inhabitants of the village… had no warning whatever, except a few who seeing the sea receding from the shore suspected a corresponding reflux, fled inland in season…Some swam single-handed with the waves. Others took their children in their arms. Others the sick on their backs, and bore them up until the water ceased from the earth…one man found the water coming into his house, seized his child and ran so as to escape the inundation entirely; but arriving on the summit of a small sand bank, he looked back and saw the whole village, inhabitants and all, moving towards him, some riding on the tops of their houses, some swimming, and all screaming most frightfully” (Armstrong
1838
: 251).
Armstrong’s account highlights the danger of tsunamis of unknown origin not associated with any local seismic activity (Atwater et al.
2015
). On this occasion, the recession of the sea, which modern studies estimate at 36?m (Lander and Lockridge
1989
), elicited two opposing responses. Unsurprisingly, children who witnessed the exposed ocean bottom took the opportunity to gather marine resources. However, those who were aware of the dangers of a rapidly receding ocean fled the scene, presumably an act that saved their lives and one that speaks of a sensitivity to the abnormal behavior of the sea. The impact on Maui included the destruction of 26 homes and the loss of two lives. Inundation distances were estimated to be around 240?m, and while actual wave heights on Maui and Hawai?i Island remain unclear, observers on O?ahu recorded waves of 2.4?m (Lander and Lockridge
1989
).
On December 1, 1860 CE, another tsunami of unknown origin struck the island of Maui. Although it did not produce any fatalities, it destroyed several homes and a wharf at the north shore valley of M?liko (Fig.?
1
). Observers estimated wave heights at Kahului, approximately 7?km to the west of M?liko, to be about 2.5?m (Anon
1860
; Lander and Lockridge
1989
). Interestingly, by the late nineteenth century, the community at M?liko had abandoned this site, though it remains unclear to what degree this, and subsequent tsunamis, contributed to the abandonment. However, coastal village abandonment after tsunami inundation did occur at four other locations on Maui in the nineteenth and twentieth century, as described below.
Hawai?i’s second deadly tsunami in this period struck on April 3, 1868 CE, when a magnitude 7.5 tsunamigenic earthquake on the south east coast of the island of Hawai?i, in the district of Ka?? (Fig.?
1
), generated the most destructive tsunami to strike the Hawaiian Islands in the nineteenth century. As reported by the Pacific Commercial Advertiser “
the tidal wave swept over the tops of the cocoanut [sic] trees along the whole line of the coast
” (Anon
1868
: 619 6?m). Measurements taken in the aftermath of the tsunami indicated wave heights of approximately 6?m. The waves destroyed 108 homes and caused 47 deaths (an additional 34 individuals died because of earthquake-generated landslides) (Lander and Lockridge
1989
). In the aftermath of the tsunami, the village of ??pua was abandoned, as visitors to the site noted that the original location lay under approximately 2?m of water due to subsidence (Ladefoged et al.
1987
).
A feature of local-source tsunamigenic earthquakes includes the amplification of wave inundation due to coastal subsidence. For example, in the aftermath of a 1975 CE local-source earthquake and tsunami on Hawai’i’s Ka?? coast researchers documented subsidence of 1.5?m on an 8-hectare shelf (Lander and Lockridge
1989
) (Fig.?
1
). Tsunami damage also extended to other parts of Hawai?i Island, including Keauhou Bay on the south-east coast (Walker
1999
) (Fig.?
1
).
On July 24, 1869 CE, a tsunami of unknown origin struck the coastal village of Nu?u in Kaup? (Fig.?
1
).
Footnote
2
Although reports do not specify the number of homes (if any) damaged or destroyed in this incident, waves inundated up to 270?m inland in certain areas, and at least one wave overtopped a 4.5?m embankment (Anon
1869
; Lander and Lockridge
1989
). Once a thriving and vibrant community, Nu?u experienced tsunami impacts in both the nineteenth and twentieth century, and after a 1946 CE tsunami it was abandoned. Like M?liko, the decline and demise of Nu?u was closely linked to destructive tsunami waves.
Hawai?i’s third and final (known) deadly nineteenth century tsunami occurred on May 10, 1877 CE, when a tsunamigenic earthquake occurred off the coast of Chile in the same general location as the 1837 CE event (Lander and Lockridge
1989
). Again, the island of Hawai?i, and Hilo in particular, suffered the greatest damage. This tsunami, which was reported at 4:45 a.m., took the lives of 5 individuals and destroyed 37 dwellings (Anon
1877
). Records revealed wave oscillations of 12?m, with an inundation distance of 92?m (Lander and Lockridge
1989
). This incident highlights a reality of Hawaiian tsunamis: that Hilo typically experiences the greatest damage and loss of life from distant-source tsunamis. While the geometry of the bay and the offshore coastal shelf contributes to the destructive potential of tsunami waves in Hilo, the coastal location of dwellings and development along Hilo Bay substantially exacerbates this problem (Chague et al.
2018
).
The last reported destructive tsunami in the nineteenth century occurred on January 20, 1878 CE, and seems to have been generated from the Aleutian Islands (although its source remains somewhat unclear). O?ahu’s north shore town of Wailua (Fig.?
1
) recorded a 3?m wave, yet Maui seems to have experienced the most significant damage (Lander and Lockridge
1989
). In M?liko, on Maui’s north shore, 8 homes and one scow were destroyed and two canoes were damaged. Halehaku, approximately 3 miles north-east of M?liko, reported two homes lost and two others damaged. At Honoman?, approximately 10 miles from Halehaku, agricultural fields (taro patches) were substantially inundated (Anon
1878
).
As noted above, M?liko had suffered damage 18?years previously during the 1860 CE tsunami. Perhaps more importantly, all three of the communities affected by the 1878 CE tsunami, M?liko, Halehaku and Honoman?, remain unpopulated to this day, although the precise causes and timing of their abandonment remain unclear. While archaeological research has uncovered evidence of village abandonment in other parts of Maui not associated with tsunami impacts (e.g., Waihe?e on Maui’s north west coast, Fig.?
1
), the coincidental timing of the abandonment of M?liko, Halehaku and Honoman? after the 1860 CE tsunami suggests a causative link.
The study of Hawaiian tsunamis in the nineteenth century reveals several interesting patterns. First, three out of 30 tsunamis (11 of which were destructive) claimed the lives of 68 individuals. Second, three locations on Maui that experienced tsunami impacts during the nineteenth century (Honoman?, M?liko and Halehaku) remain largely depopulated. Third, although most of the historically recorded tsunamis arrived with little or no warning, they produced surprisingly few fatalities. The low death rate may be explained by three factors: Hawai?i’s rapid population decline in the nineteenth century; the rural nature of the population (which concealed actual tsunami deaths due to a lack of accurate reporting); and, perhaps, inherited traditional knowledge of the signs of approaching tsunamis, which has been seen recently in other tsunami-impacted areas (Stannard
1989
; Goff and Dudley
2021
).
3.2
Twentieth century tsunamis in the Hawaiian islands
During the twentieth century, a number of destructive and deadly tsunamis impacted coastal areas of the Hawaiian archipelago. More precise records of economic loss and fatalities, combined with demographic shifts toward population centers (where fatalities would not go unreported), provide a portrait of tsunami impacts in Hawai?i that is more detailed than that available for the previous century. The twentieth century also saw the development of a life-saving advanced tsunami warning system (Walker
1999
).
Hawai?i?s first significantly destructive twentieth-century tsunami arrived on February 3, 1923 CE, shortly after 4:00 p.m., and originated from a tsunamigenic earthquake off the coast of the Kamchatka Peninsula, Russia. Hilo recorded seven waves, with heights reaching up to 3.6?m, and one fatality. At Kahului, observers reported wave heights of 3.5?m and substantial damage. Although observers recorded waves at Haleiwa, O?ahu (Fig.?
1
) of 3.7?m, residents did not report any damage or loss of life. The 1923 CE Kamchatka tsunami took only one life, but economic losses totalled nearly $1.5 million dollars (over $26 million in 2023 dollars; Lander and Lockridge
1989
; Shepard et al.
1950
).
Scientists at the newly developed Hawai?i Volcano Observatory (HVO), who learned of the possibility of a destructive tsunami well in advance of its arrival, notified harbor masters at key port facilities across Hawai?i, but, tragically, their warnings were dismissed. Hawaii at the time lacked a formal system to broadcast tsunami warnings (Goff and Dudley
2021
), but the 1923 CE Kamchatka tsunami demonstrated the potential for a warning system, and one was developed in the aftermath.
In the early morning hours of April 1, 1946 CE, Hawai?i experienced its most destructive historical tsunami when a Mw 8.6 earthquake occurred at 2:00 a.m. Hawai?i time in the Aleutian trough south of Unimak Island (Lopez and Okal
2006
; Keating et al.
2004
; Chague et al.
2018
). The first wave struck the island of Kaua?i at 6:00 a.m., Honolulu at 6:33 a.m., and Hilo at 7:06 a.m. (Shepard et al.
1950
). Fortunately, the small size of the first wave alerted the community and caused limited damage. By the time the 3rd, and largest, of the 9 waves recorded at Hilo (where the most severe damage occurred; Fig.?
2
), came ashore, many people had escaped, no doubt preventing a larger loss of life (Chague et al.
2018
: 320). Nonetheless, the 1946 CE Aleutian tsunami killed 159 Hawai?i residents, most of them on Maui and Hawai?i Island, particularly in and around Laup?hoehoe and Hilo (Goff and Dudley
2021
; Chague et al.
2018
). Estimates of economic damage to the archipelago exceed $25 million dollars ($370 million in 2023 dollars) (Shepard et al.
1950
).
The 1946 tsunami provided an opportunity for scientists in Hawai?i to study details of impacts on various parts of the archipelago. For example, F.W. Shepard, who at the time was vacationing with his wife on O?ahu, and who narrowly escaped the tsunami, recorded a number of important features of this tsunami (Shepard et al.
1950
; Goff and Dudley
2021
). He recorded wave heights of 13.7?m at H??ena on Kaua?i’s north coast and noted that a coral block approximately 4?m in diameter had been transported 152?m inland (Shepard et al.
1950
). Perhaps more importantly, he linked wave runups in certain areas to topographical and geomorphological features, recognizing that where fringing coral reefs were present, wave heights were up to 5?m lower than in areas that lacking such features. The wave heights he recorded at Waikolu, Moloka?i (Fig.?
1
), exceeding 16?m, were perhaps the largest in the archipelago during this event, and he provided important observations about the relationship between topography, geomorphology, wave runup and destructive potential. Subsequent researchers have followed suit by studying the relationship between these variables and tsunami impacts along other Hawaiian coasts (Whelan and Keating
2004
).
With a relatively large geographical area to cover, and relatively few resources to undertake such a monumental task, Shepard et al. (
1950
) findings include some that are inaccurate or cursory. This should not be seen as an indictment of the quality of their work but as a reminder of the need for additional tsunami and paleotsunami research. For example, at Waihe?e, on Maui’s north west coast, Shepard et al. (
1950
) recorded the wave height as 7?m but noted no additional damage to any homes or the dairy facility located there. Ethnographic work from 2004 to 2008 in Waihe’e revealed the loss of at least three homes in this area (H. Shimoda, M. Molina, and J. Ka’ili’ehu, pers. comm. 2004?2008).
At Nu’u, on Maui’s south east coast, a recent ethnographic study of the impacts of the 1946 CE tsunami has provided substantive insights beyond those recorded by Shepard et al. (
1950
). While Shepard et al. (
1950
) noted a 3?m wave at Nu’u, survivor testimony reveals changes to patterns of shoreline accretion and the abandonment of this village after the 1946 CE tsunami (H. Starr, and S. Ka’ai, pers. comm. 2009). Site visits to tsunami-impacted areas, such as those studied by Shepard et al. (
1950
), remain a vitally important resource for coastal land managers. But multi-proxy approaches, including the capture of survivor testimony, contribute to a clearer understanding of wave intensity and general tsunami destructiveness.
As at Nu?u, the 1946 CE tsunami also prompted the abandonment of the village of Shinmachi, located along the coast of Hilo Bay (Fig.?
1
). A 2018 study of the now-abandoned Shinmachi village, where many of the fatalities occurred, reported 1946 CE tsunami sediments up to 12?cm thick (Chague et. al.
2018
). Out of the tragedy of the 1946 CE tsunami, the Pacific Tsunami Warning Center (PTWC), which employs a complex network of detectors combined with sirens across the archipelago, emerged. This advanced warning system, the first of its kind, has saved countless lives across Hawai?i and the North American west coast.
Footnote
3
Eleven years later, on March 9, 1957 CE, a Mw 8.3 tsunamigenic earthquake, also from the Aleutian islands, struck the Hawaiian Islands. Observers reported wave heights on Kaua?i of 16?m; the other islands recorded smaller waves (Lander and Lockridge
1989
; Keating et al.
2004
). Polol? Valley, on Hawai?i Island, for example, measured runups of 9.8?m above mean sea level (Chague-Goff et al.
2012
: 84). Despite the destruction of at least 54 homes across the archipelago, and over $300,000 in damage to coastal infrastructure (equivalent to over $3 million today), the evacuation of coastal residents during the 1957 CE Aleutian tsunami, which prevented any loss of lives, testifies to the efficacy of the PTWC (Lander and Lockridge
1989
: 44; Keating et al.
2004
).
Footnote
4
On May 22, 1960 CE, a Mw 9.4?9.6 tsunamigenic earthquake hits the Hawaiian Islands from Valdivia, Chile, the approximate location of the 1837 CE tsunami described above. Hilo suffered substantial damage. The largest wave, the third in the set, arrived at 1:04 a.m. as a 6.1?m bore, which rose to 10.7?m as it arrived on shore. Interestingly, studies that have compared sedimentary deposition in Hilo could not distinguish between the 1946 CE and 1960 CE tsunamis because of the similarity of the depositional area and the behavior of the waves on land, despite the fact that the two tsunamis came from nearly opposite directions (Chague et al.
2018
: 331). This was largely the result of wave resonance inside Hilo harbor (Fig.?
3
).
While other parts of the archipelago suffered damage, Hilo once again bore the brunt of the destruction (Lander and Lockridge
1989
; Whelan and Keating
2004
: 77). This tsunami’s high casualty count suggests that implementation of the early warning system was flawed. Tsunami researchers noted two possible reasons for this failure. First, false alarms had become common in the early years of the tsunami warning system, leading to a sense of complacency (Walker
1999
). Second, the tsunami’s arrival early in the morning could have exacerbated this sense of complacency (Chague et al.
2018
).
The last fatal tsunami of the twentieth century occurred on November 29, 1975 CE, in the Halap?-Apu? area, approximately 39 miles south of Hilo. The 1975 CE Halap?-?pua tsunami was produced by two local earthquakes, a M 5.7 foreshock at 3:55 a.m. followed by a M 7.7 earthquake at 4:48 a.m. (Goff et al.
2006
; Richmond et al.
2011
; Nettles and Ekstrom
2004
). A Boy Scout troop, camping near the base of a cliff and concerned about the possibility of a rock slide, moved to a location closer to the coast. Shortly after the earthquake, a wave estimated at 5?m above sea level inundated their new camping area to a distance of 250?m inland, transporting debris and boulders and killing one Boy Scout and the troop’s leader. Nineteen other Boy Scouts were also injured (Lander and Lockridge
1989
). Although locally sourced, the Halap?-?pua earthquake and tsunami-impacted large areas of the Ka??, or the south-east coast of Hawai?i Island. Extensive areas were affected by coastal subsidence, which caused approximately $1 million dollars in damages (over $5.2 million in 2023 dollars).
Two recent studies, which included both field surveys and detailed ethnographic research, provide a clear picture of this tsunami and clarify previously unknown dimensions of this event. For example, several waves transported substantial quantities of material as both suspended and bed load, and survivors recounted three powerful waves (Goff et al.
2006
; Richmond et al.
2011
). Both studies highlight the value of multi-proxy approaches that include the collection and analysis of field data and the incorporation of survivor narratives.
In summary, the twentieth century witnessed a dramatic increase in the number of tsunami-related fatalities, from 68 known tsunami deaths in the nineteenth century to 222 in the twentieth century. Economic losses from tsunamis in the twentieth century were also substantial, exceeding $580 million (adjusted for inflation). Although recorded fatalities have increased (likely due to population growth along the coast), the development of an advanced warning system has no doubt saved many lives, and Hawai?i has not experienced a direct tsunami-related death in nearly 50?years. However, the tsunamis that have struck the Hawaiian Islands since 1975 CE have been notably smaller than those of previous eras.
3.3
Hawaiian tsunamis in the twenty-first century
During the twenty-first century, four measurable tsunamis have impacted the Hawaiian Islands. All caused only minor damage and produced no direct fatalities. The first of these involved an 8.3 Mw tsunamigenic earthquake on November 15, 2006 CE, which originated in the Kuril Islands. In Hawai’i, the tsunami waves measured only 76?cm at Kahului and 49?cm at Hilo (Munger and Cheung
2008
).
The next tsunami to strike the Hawaiian Islands, on February 27, 2010, was produced by a 8.8 Mw tsunamigenic earthquake off the coast of Chile (Roessler and Lipton
2010
). The Pacific Tsunami Warning Center anticipated waves in the range of 1.8?m to 3.0?m and issued an evacuation order for the City of Honolulu, the first in 16?years. At Honolulu Harbor, wave heights measured only 45?cm, which led to public skepticism about the efficacy of the tsunami warning system (Dwyer
2010
).
In the early morning hours of March 11, 2011 CE, Hawai?i experienced its largest tsunami to date of the new century. Generated by a Mw 9.0 earthquake off the T?hoku-oki region of Japan, this tsunami took the lives of over 16,000 people in Japan. The first waves reported in Hawai?i arrived in the early morning hours, beginning around 3:00 a.m., with the largest wave measuring 1.8?m at N?wiliwili (Cheung et al.
2013
). The fourth and largest wave of this tsunami measured 2.07?m and ripped up trees while flooding low-lying areas in the town of Kahului, with an inundation distance measured at 614?m (Osher
2011
). At Waihe?e on Maui, the tsunami inundated up to 150?m inland depositing a discontinuous layer of sand and cobbles some 12?m inland from the coastal berm ridge (Fig.?
4
). On Hawai?i Island, four hotels and a historic structure, the Hulihe?e Palace in Kailua-Kona, were damaged, with financial losses across the archipelago estimated at $7.5 million ($8.7 million in 2023 dollars; Sakahara
2011
).
Modelled data for the 2011 CE tsunami have shed additional light on the nature of Hawaiian tsunamis. Cheung et al. (
2013
) research demonstrated that the complex wave patterns seen in the Hawaiian archipelago generate relatively long-lasting resonance wave arrays, potentially amplifying tsunami impacts and complicating mitigation strategies. This research demonstrates the need for both field data collection and modelling to better understand, constrain and (for future tsunami) predict the impacts of tsunamis on Hawaiian coastlines.
Hawai?i’s most recent (at the time of publication) tsunami came in the early morning hours of January 15, 2022 CE, after the submarine volcanic eruption of the Hunga-Tonga Hunga-Ha’apai Volcano, Tonga. Across the archipelago, observations revealed wave heights around 1.0?m, including Hanalei on Kaua?i and M?nele Harbor on L?na?i (Sakahara
2022
). Runups of 4.0?m and a 20?m inundation distance were recorded at Nu?u, on Maui’s south east coast (Terry et al.
2022
). The largest wave recorded occurred in the Kailua-Kona area of Hawai?i Island, where a 1.3?m wave inundated Kai Opua Canoe club and destroyed approximately 80% of the inventory of one local business, causing approximately $75,000 in damages (Sakahara
2022
). Although South Pacific tsunami sources are somewhat rare in the historical record, studies of the 2022 Tongan tsunami might prove particularly helpful in gaining a clearer understanding of the fifteenth century Kuwae, Vanuatu, volcanic eruption and tsunami discussed below (Goff et al.
2012
).
3.4
Pre-historic holocene tsunamis in Hawai’i
Perhaps the most surprising aspect of Hawaiian Holocene tsunamis is the small number of events discovered by researchers in the ethnographic or sedimentary records, suggesting a substantive knowledge gap for the Hawaiian archipelago. The most extensively studied Holocene deposits come from a sinkhole on Kaua?i’s south shore, the Makauwahi Cave system near Po?ip?, which lies 100?m from the coast at 7.2?m above sea level (Butler et al.
2014
). In their study of the paleoecological dynamics of the Makauwahi cave system, Burney and others discovered tsunami deposits 80?cm thick initially dated to between 1425 and 1660 CE (Burney et al.
2001
). Butler et al. (
2014
) subsequent Uranium?Thorium (U?Th) dating analyses indicated that the Makauwahi Cave tsunami probably dated to the second half of the sixteenth century (later updated to 1551?1593 CE; Butler et al.
2017a
), which the authors linked to an earthquake source near Sedanka Island in the Aleutian Islands. While Butler et al. (
2014
) research leaned heavily toward an Aleutian Islands source, they point out that a local submarine landslide could have generated a wave of sufficient magnitude to generate these deposits.
Perhaps most importantly, the research conducted by Butler et al. (
2014
,
2017b
) led to a re-examination of the tsunami threat to Hawai?i posed by the Aleutian Islands. Through modelling, Butler et al. (
2017b
) concluded that offshore faults in the Aleutian Islands, combined with the proximity of Hawai?i to the Aleutian Islands and the geometric focusing that occurs during large seismic events, poses a triple threat to the Hawaiian archipelago. Although future research at the Makauwahi Cave site may demonstrate a local, as opposed to an Aleutian Islands, source for the sixteenth-century event, Butler et al. (
2017b
) have clarified our understanding of the threat presented by Aleutian Island tsunamigenic earthquakes.
Following the work of Butler et al. (
2014
), the US Geological Survey began additional paleotsunami research at multiple locations across Hawai?i (LaSelle, pers. comm. 2015). This research, which began with a reconnaissance of 13 sites across the archipelago, conducted extensive research at Anahola on Kaua?i, Kahana on O?ahu, and Polol? on Hawai?i Island. This research yielded sedimentary evidence of one, or possibly two, distant source tsunamis that probably originated in the eastern Aleutian Islands. Evidence included sand beds with normal grading that thinned inland and with sharp lower contacts (La Selle et al.
2020
). Each site contained tsunami deposit(s) that could be traced significant distances inland, specifically 650?m at Anahola, 450?m at Kahana, and 500?m at Polol? (La Selle et al.
2020
). Conclusive evidence of tsunami inundation, like that found at these various sites across the Hawaiian archipelago, provides a foundation upon which coastal land managers can better understand mitigation options.
While sedimentary evidence of tsunamis in the Hawaiian archipelago during the Holocene is limited, ethnographic and archaeological research can potentially shed light on events which have occurred in the past 1000?years, since the beginning of human settlement of the archipelago. The account recorded by the ethnographer Martha Beckwith (Beckwith
1982
) provides one of the most detailed legends about a significant marine inundation event. According to this account, the chief Nu?u, sometimes known as Kahinali?i, lived during the kaiakahinali?i or, literally, the time of the bringing down of the chiefs.
Footnote
5
According to legend, Nu?u survived this catastrophic event on a double-hulled canoe equipped with living quarters (
Wa?ahalauali?iokamoku
). When the great wave receded, Nu?u’s canoe came to rest on the summit of Mauna Kea on Hawai?i Island, whereupon he made offerings to the deities. Although there exist clear similarities with the biblical story of Noah (perhaps reflecting later missionary influences), the clear use of the term ‘
kai,
’ or ocean water, in the description of the event (as opposed to ‘
wai
’ or freshwater), indicates that the inundation came from the ocean, not rainfall.
This legend seems to suggest an event that dramatically restructured the Hawaiian social hierarchy, particularly the ruling
ali?i
class (Beckwith
1982
). Research throughout the South Pacific has demonstrated the historical validity of legends of a powerful tsunami that occurred in the fifteenth century and is linked to contemporaneous sedimentary evidence (Cain et al.
2019
; Goff et al.
2012
; Lavigne et al.
2021
). Such evidence highlights the value of oral history, including recitations of legends that reveal changes in the social fabric in the aftermaths of such catastrophic events.
Archaeological research published from H?lawa Valley on Moloka?i identified a culturally sterile sand layer fining inland that caps a habitation layer (Kirch and McCoy
2007
). Considering its close proximity to the coast, additional research to determine if the culturally sterile sand derives from a high energy marine inundation event seems particularly warranted. Recognition of tsunami deposits in the archaeological record would prove particularly helpful in identifying both the frequency of this type of disaster and human responses to such events (e.g., McFadgen and Goff
2007
; Salazar et al.
2022
).
3.5
Pleistocene tsunamis: mega-tsunami versus lithospheric flexure
Researchers have published a substantial body of material on pre-Holocene marine sediment deposits found on the islands of L?na?i, Moloka?i and Hawai?i (Moore and Moore
1984
; Moore et al.
1994
; Johnson and Mader
1995
; McMurtry et al.
2004
; Webster et al.
2006
; Moore
2008
). Moore and Moore (
1984
) and Moore and Moore (
1988
) identified a layer of fragmented coral, basalt boulders and sand and shell fragments (known as the Hulopo?e gravel), first identified in the nineteenth century on L?na?i, as mega-tsunami deposits that date to 105?ka BP, with wave runups that reached 375?m above modern sea level. Other research on L?na?i identified additional material dated to between 240 and 200?ka BP, positioned 46?60?m above modern sea level (Moore et al.
1994
).
Moore et al. (
1994
: 966) cited several lines of evidence to support their mega-tsunami hypothesis, including an absence of coral clasts in growth positions and the fact that no deposits contained sedimentary sorting, from which they inferred deposition under turbulent conditions. In their analysis of the data, McMurtry et al. (
2004
) noted the fragmented shell material formed a blanketing depositional pattern, suggestive of tsunami deposition. Johnson and Mader (
1995
) and McMurtry et al. (
2004
) posited that the source of these proposed mega-tsunamis were two catastrophic submarine failures off Hawai?i Island’s Mauna Loa volcano, known as Alika I and Alika II, that occurred approximately 105?ka BP and between 240 and 200?ka BP, respectively.
Several scholars, however, have questioned the mega-tsunami hypothesis (Grigg and Jones
1997
; Rubin et al.
2000
; Keating and Helsey
2012
). While none discount the possibility that very large tsunamis have impacted the Hawaiian Islands, they reach different conclusions about deposition of the Hulopo?e gravel and similar deposits. Principal among these is lithospheric flexure, which can uplift deposits, leaving them unmodified and in their original location, which would not happen if the deposits had been deposited by a tsunami. Evidence of such intact deposits includes coral found in growth position at relatively high elevations and the increasing age of coral deposits with elevation, which sceptics of the mega-tsunami hypothesis suggest are indicative of lithospheric flexure (Grigg and Jones
1997
). Perhaps the most important result of this debate lies in its focus on the frequency and destructive capacity of flank collapse, a catastrophic failure of the coastal portion of the shield volcano. As a result, these contributions to tsunami research have helped broaden our understanding of the risk and exposure Hawaiian coasts face from locally generated, catastrophic, high energy marine inundation events.